Prime mortgage borrowers are struggling to keep up their payments – the proportion of top-quality loans held in asset-backed securities that are at least one month in arrears has risen 50 per cent.

A report on Monday by Standard & Poor’s notes that, at 3.24 per cent, the percentage of delinquent loans to prime borrowers at the end of September compared with a year earlier is at its highest since the ratings agency developed its index in 2000.